This invention pertains to symbol generators and, more particularly, to the loading of the line buffer memories of such generators. There are presently available symbol generators which are capable of generating lines of symbols or characters for use in television display systems.
When, for example, English text is to be displayed on a television screen one need only be concerned with whether the text is represented in upper or lower case, assuming that a particular font is being used. In such case, it makes no difference what the succeeding and preceding characters are with respect to a given character; however, in some languages such as Arabic, the situation is completely different. In Arabic, many characters have as many as four different forms. For example, a given character may have one form when it stands alone, i.e., it is neither preceded or followed by a space. It has another form if it is both preceded and followed by a space. It has a third form if it is preceded by a space and followed by non-space, and it has a fourth form if it is followed by a space and preceded by non-space symbol. Therefore, the font for the Arabic alphabet is quite large.
Conventional character generators used in television normally have a keyboard wherein each key is associated with a given character. Just as with a typewriter, there can be case shifting in a character generator to provide both upper and lower case characters. Thus, every form of the character is associated with one or possibly two keys, i.e., for instance, the letter "A" can be a capital "A" or a small "a". The two keys associated with these two variations are the basic key for the letter "A" and the case shift key. Thus, it is possible to minimize the size of the keyboard. With respect to the Arabic language, it has heretofore been necessary to provide separate keys for each one of the characters and for each one of its variations. Thus, in many cases it has been necessary to provide keyboards wherein there are four separate keys associated with a given character wherein each key generates one of the four possible variations of the character. Because of the size of the Arabic alphabet and all the associated variations, the size of the keyboard required to generate high quality characters for television display becomes excessively large. In addition, a burden is placed on the operator in that considerable dexterity and memory are required to operate such a keyboard.